Interspecific hybidization of Gardenia jasminoides Ellis and G. thunbergia L.

ABSTRACT

A cultivar of  Gardenia jasminoides,  characterized by longevity and consistent production of seed, and  G. thunbergia,  recognized to have resistance to nematode damage, have been hybridized to combine the desirable characters of both species and facilitate production of improved cultivars.

VARIETY DENOMINATION

The resulting Fl plant(s) are herewith identified as Gardenia HybridOne.

BACKGROUND AND SUMMARY OF THE INVENTION

Gardenia (Gardenia jasminoides) has been a favorite landscape plant inthe warmer areas of the United States for more than a century.Popularity of the species has been encouraged, in large part, by theattractiveness of the plants and the allure of the pleasantly aromaticflowers. Additionally, the species is quite adaptable to variouscultural methods and has modest to long-term life expectancy. There is aconsistent lack of seed production in most cultivars despite frequentproduction of pollen and pistillate structures which leads to thepresumption that most present-day cultivars have originated as asexualdeviants. The species has few important cultural problems other thannematode infestation for which no cultivars of G. jasminoides are knownto exhibit tolerance or resistance. Thus, a sizeable share of the plantsproduced for retail sale are now grafted onto stocks of G. thunbergia,the only recognized nematode-resistant species of the genus and theprice to consumer must reflect this additional production cost.Unfortunately, this rootstock species is intolerant of freezingtemperatures and, thereby, limits the range of successful, outdoorculture of grafted plants to zone 8 or warmer.

The discovery of a reliable seed-producing cultivar of G. jasminoides,i.e. “Star Bright” (U. S. Pat. No. 8,887) (SB), made possiblehorticultural improvement through controlled breeding. In 2004, crosspollinations on SB were made with pollen from G. thunbergia and, in duecourse, a population of four seedlings was obtained. These four plantshave been reproduced repeatedly (asexually) by rooting cuttings and havenow flowered and shown to have fertile pollen as well as beingself-fertile. Flowers have the pleasing fragrance typical of the genusGardenia.

Flower formation in the pollen parent plant (G. thunbergia) is uniqueand typically begins with the appearance of a calyx tube nominally 12 mmin diameter and 10 cm in length with a ring of wings each about 3×10 mmat the top. Eventually, a split near the middle of this lengthy tubepermits extrusion of the closed flower bud and subsequent extension ofthe corolla tube to approximately 5 cm with the bud at the apical end.Soon thereafter, a single whorl of (usually) eight white petals unfurlswith the pistillate structure extending about 1 cm above the plane ofthe petals. The apical ends of the anthers, spaced alternately with thepetals, partially separate from the petals at anthesis and remainupright thereafter attached in the upper throat of the corolla. Asillustrated (see FIG. 1 and 2) flower development in the hybrid plant isquite different from that of the pollen parent and quite similar to thatof the pistillate parent (SB). The calyx tube is absent with a muchshorter (than G. thunbergia) corolla tube but still considerably longer(to 5 cm) than in the pistillate parent plant. Anthers are recurvedoutward after anthesis and remain attached in the throat of the corolla(FIG. 3). The pistillate structure protrudes a cm above the plane of thewhorl of petals and appears to be divided in two parts with a strip ofexposed tissue dividing the two halves as in S. B. There is abundantpollen produced by the hybrid (FIG. 4). The typical fragrance of thegenus is retained in the hybrid and resembles that of the pistillateparent. Thus, the flower formation of the hybrid includes features fromeach of the two parent plants but not a predominance of characters fromeither. Leaves and stems of hybrid plants are indistinguishable fromthose of the pistillate parent (FIG. 5 and 6) while the pollen parenthas leaves characteristically bellows-shaped. Mature plants may reach1.5 m×1.5 m in size with moderately open branching as in the pistillateparent. Self-pollination in the hybrid plant has resulted in seed podformation identical to that in SB and successful out-cross pollinationsand seed production in several cultivars of G. jasminoides demonstrated.

The combined persistence of the original pistillate parent plant (SB),now more than thirty years old, and the acknowledged pest resistance ofG. thunbergia, should contribute significantly to development ofimproved cultivars of gardenia.

FIG. 1. Side-view of hybrid bud and extended corolla tube

FIG. 2. Mature hybrid flower with a single whorl of petals

FIG. 3. Top view of hybrid petals after anthesis

FIG. 4. Side view of pistillate structure showing exposed suture

FIG. 5. Upper side view of hybrid plant leaves

FIG. 6. Bark/bud features of hybrid plant stems

REFERENCES

Cook, A. A. 1994. Gardenia jasminoides var. Star Bright. U. S. Pat. No.8,887. 6 p. Huxley, A., M. Griffiths and M. Levy. 1992. The New RoyalHorticultural Society Dictionary of Gardening. The MacMillan PressLimited, London pp. 366-367.

1. Hybridization of Gardenia jasminoides×G. thunbergia and theproduction of cultivars derived therefrom.